1. Field of the Invention
The present invention relates to an apparatus for automatically cleaning semiconductor wafers in a one-by-one manner (single wafer transfer system), including a wafer erection assembly, a brush cleaning bath, a plurality of wafer cleaning baths adapted to clean one wafer at a time by having each wafer steeped (e.g. soaked thoroughly) in a generally vertical orientation in the cleaning liquid, and a wafer handling apparatus consisting of a robot arm.
2. Description of the Prior Art
In the semiconductor device manufacturing technology, the impurities adhering to the surfaces of the semiconductor wafers are known to adversely affect the properties of the resulting semiconductor devices.
Therefore, a cleaning step is included in the semiconductor wafer manufacturing process. In the cleaning step, the wafers are cleaned in various methods which are classified broadly into two groups: mechanical cleaning methods and chemical cleaning methods.
The mechanical cleaning methods include the brushing method wherein the impurities adhering to the wafer surfaces are directly brushed off by means of appropriate brushes, the flushing method wherein the impurities are removed from the wafer surfaces as pressurized fluid from an injection nozzle is applied to the wafer locally or entirely, the ultrasonic cleaning method wherein the wafers are submerged in a liquid and the impurities are vibrated to detach from the wafer surfaces as ultrasonic waves are applied to the wafers.
The chemical cleaning methods include the methods wherein the impurities adhering to the surfaces of the wafers are removed as they are chemically dissolved by various chemicals and enzymes. There are other cases wherein a chemical cleaning method is combined with a mechanical cleaning method.
In the field of semiconductor manufacturing, the recent tendency of ever increasing density in semiconductor device has favored enlargement of the semiconductor wafer diameter. As the result, the conventionally adopted method of cleaning a plurality of wafers at a time while they are contained in a wafer carrier imposes heavy labor on the human attendants.
Also, if the wafers are carried in the carrier, the wafers are contaminated with particles and the like which they receive from the carrier due to contact of the wafers with the carrier.
Furthermore, if the wafers after polishing are temporarily stocked to wait until the next cleaning stage is ready to receive them, the surfaces of the wafers are dried and the impurities may remain or be redeposited adhering to the wafer surfaces.
The present invention was contrived in view of the above problems, and it is, therefore, an object of the invention to provide an automatic wafer cleaning apparatus which is capable of automatically cleaning the wafers one by one after they are finished with the polishing treatment, so that it would become possible to do away with the conventional carriers (realization of carrier-less operation), reduce the necessity of human labor involvement, and improve the product quality.
To make the most of such an automatic wafer cleaning apparatus, it is desirable that the wafers, after being polished, are transported to the automatic wafer cleaning apparatus through a fluid, e.g., pure water), by means of the fluid stream so that the wafer is not allowed to dry during the transportation. To convey the wafers by fluid stream, the wafers must be oriented horizontally in the stream. Therefore, if the automatic cleaning apparatus is designed such that the wafers are held vertically by the wafer handling apparatus such as a transportation robot as they are transported one by one, then the wafers which are brought in by the fluid stream, maintaining the horizontal orientation, must first be erected to a vertical orientation before each of them can be held vertically by the robot arm.
Therefore, it is also an object of the invention to provide a method and an apparatus for erecting a wafer vertically after it has been brought to the cleaning apparatus in a horizontal posture, so as to enable the wafer to be readily held vertically by the robot arm.
The surface of a wafer which has been polished is stuck to by particles, and to remove the particles by brush cleaning, it is necessary for an automatic cleaning apparatus of single wafer transfer system to have the wafer stand vertically when it is brushed.
Therefore, it is also an object of the invention to provide the automatic single wafer transfer type cleaning apparatus with a brush cleaning assembly which is capable of brushing both faces of a vertically held wafer at once and at a high efficiency.
Furthermore, in the automatic single wafer transfer type cleaning apparatus, since the wafer is generally held vertically as it is transferred it is necessary that the wafer is held vertically and stably when it is steeped in the cleaning liquid of each cleaning bath.
Therefore, it is a further object of the invention to provide wafer cleaning baths which are capable of allowing each wafer to be steeped vertically and held stably in the cleaning liquid for cleaning operation.
The present invention further provides the cleaning apparatus with a transportation robot as a wafer handling apparatus which can hold the wafers vertically and transport them one by one to thereby attain the automatic single wafer transfer type cleaning operation.